What are colour fringing, distortion and edge sharpness?
Colour fringing means coloured edges at areas of strong contrast, such as a dark edge against a bright background. It can occur because lenses do not reproduce all colours of light in exactly the same way. The technical term is chromatic aberration. Special glass types can help, but their presence alone does not tell you how effectively the complete optic controls this error.
Colour fringing means coloured edges at areas of strong contrast, such as a dark edge against a bright background. It can occur because lenses do not reproduce all colours of light in exactly the same way. The technical term is chromatic aberration. Special glass types can help, but their presence alone does not tell you how effectively the complete optic controls this error.
Distortion, by contrast, changes shapes. A straight line may appear to bow inwards or outwards, for example. The image can still be sharp. Another effect is called field curvature: the areas of best focus do not all lie in the same plane. The centre and edges may then appear differently sharp.
Edge sharpness therefore depends on several characteristics. Magnification, eye position and viewing conditions also influence it. Photographs taken through a riflescope have limited value for comparisons. The camera can add its own colour fringes, blur or distortion. An error visible in the photograph need not come from the scope alone.